Catalase is an enzyme which catalyzes a reaction in which hydrogen peroxide decomposes into water and oxygen. Hydrogen peroxide aqueous solution is widely used as an antiseptic or a disinfectant. After the completion of disinfection, the hydrogen peroxide solution can be easily removed with water, and is spontaneously decomposed as time progresses, and therefore, is widely used as a disinfectant for food. However, it is desired that hydrogen peroxide is completely decomposed and removed after use, because reactive oxygen species generated from any remaining hydrogen peroxide have a possibility of causing cell aging or cancer. Catalase is extremely useful for the decomposition of hydrogen peroxide, because no additional chemical substance is needed for the decomposition. Actually, catalase is used in decomposing and removing hydrogen peroxidase remained after bleaching of cotton or in food. Catalases derived from microorganisms (patent references 1 to 5) and catalases derived from animals, such as porcine or bovine liver catalase, are known.
Among such known catalases, catalase produced by a filamentous fungus Aspergillus niger or porcine liver catalase is widely used for industrial use. However, it is known that these catalases exhibit low thermostability and the remaining activity thereof after the treatment at 70° C. for 30 minutes was approximately 10% (patent reference 6). In particular, for the use of textile processing, food processing, or the like, catalase having thermostability higher than those of conventional catalases is desired, because hydrogen peroxide has to be decomposed at a high temperature. As thermostable catalases, catalases produced by Aspergillus terreus (patent reference 6), Acremonium alabamensis (patent reference 6), Thermoascus aurantiacus (patent reference 6), Scytalidium thermophilum (patent reference 7), Humicola insolens (patent reference 7), and genus Thermomyces (patent reference 8) have been reported.
It is known that filamentous fungi have an extremely high activity of secreting proteins, and are suitable as a host to produce a recombinant protein such as enzymes. Therefore, if a thermostable catalase gene can be introduced into a filamentous fungus and the thermostable catalase can be highly expressed as a recombinant protein, it is expected that the thermostable catalase can be produced at extremely high productivity in comparison with a wild type. With respect to the production of recombinant proteins, it has been reported that recombinant proteins could be produced in filamentous fungi classified into genus Aspergillus (patent reference 9), Penicillium (patent reference 10), Humicola (patent reference 11), Trichoderma (patent reference 12), or Acremonium (patent reference 13).
When a recombinant protein is expressed in these filamentous fungi as a host, all exogenous genes introduced into the host are not necessarily expressed. In general, it is considered preferable that the origin of an exogenous gene to be introduced is related to that of a host as closely as possible, in view of codon usage. For example, in the case that Humicola insolens was used as a host to express endoglucanase as a recombinant protein, a significant amount of endoglucanase was expressed when an NCE4 or NCE5 gene derived from Humicola insolens was introduced into Humicola insolens (patent references 14 and 15). By contrast, little amount of endoglucanase was expressed when an RCE I gene, which was derived from Rhizopus oryzae and had an amino acid sequence showing a high identity with those of NCE4 and NCE5, was introduced into Humicola insolens (patent reference 16). Further, in the case that Aspergillus awamori was used as a host to express glucoamylase as a recombinant protein, the introduction of a glucoamylase gene derived from Aspergillus niger resulted in high productivity (4.6 g/L), but the introduction of a glucoamylase gene derived from Humicola grisea resulted in low productivity (0.66 g/L) (non-patent reference 1). Furthermore, in the case that α-amylase was expressed as a recombinant protein, the introduction of an α-amylase gene derived from Aspergillus oryzae into Aspergillus oryzae as a host resulted in high productivity (12 g/L), but the introduction of the α-amylase gene derived from Aspergillus oryzae into Trichoderma viride resulted in only a productivity of 1 g/L (non-patent reference 1). These results show that, when a significant amount of recombinant protein is to be expressed, it is preferable to introduce a gene derived from a filamentous fungus which is the species same as or related to that of a host.
When a filamentous fungus is used as a host to express a large amount of thermostable catalase as a recombinant protein, it is considered preferable that the origin of a thermostable catalase gene to be introduced is closely related to the filamentous fungus as the host, as described above. However, with respect to the isolation of thermostable catalase genes, only a catalase gene derived from Thermoascus aurantiacus (patent reference 17) and a catalase gene derived from Scytalidium thermophilum (patent reference 18) have been reported. Thermostable catalase genes have not been isolated from filamentous fungi developed as a host for protein production, such as genus Aspergillus, Penicillium, Humicola, Trichoderma, or Acremonium, and therefore, it was very difficult to express thermostable catalase as a recombinant protein with high productivity.    [patent reference 1] Japanese Unexamined Patent Publication (kokai) No. 55-135588    [patent reference 2] Japanese Unexamined Patent Publication (kokai) No. 60-083579    [patent reference 3] Japanese Unexamined Patent Publication (kokai) No. 63-003788    [patent reference 4] Japanese Examined Patent Publication (kokoku) No. 49-004956    [patent reference 5] Japanese Unexamined Patent Publication (kokai) No. 2-076579    [patent reference 6] Japanese Unexamined Patent Publication (kokai) No. 5-153975    [patent reference 7] Japanese Translation Publication (Kohyo) No. 6-506347    [patent reference 8] Japanese Unexamined Patent Publication (kokai) No. 10-257883    [patent reference 9] International Publication WO 97/034004    [patent reference 10] International Publication WO 2000/068401    [patent reference 11] International Publication WO 98/003667    [patent reference 12] International Publication WO 98/011239    [patent reference 13] Japanese Unexamined Patent Publication (kokai) No. 2001/017180    [patent reference 14] International Publication WO 98/003640    [patent reference 15] International Publication WO 2001/090375    [patent reference 16] International Publication WO 2000/024879    [patent reference 17] Japanese Unexamined Patent Publication (kokai) No. 2004-261137    [patent reference 18] U.S. Pat. No. 5,646,025    [non-patent reference 1] Norihiro TSUKAGOSHI, Kumikae Tanpakushitsu Seisan-hou (Production of recombinant proteins), Japan Scientific Societies Press, pp. 94-95